THE INFLUENCE OF COMPRESSIVE LOADS ON FATIGUE-CRACK PROPAGATION IN METALS

An experimental study on Al alloy 7475-T7351 was conducted to determin e the influence of compressive loads on fatigue crack propagation. The investigation was based on the determination of the crack propagation stress intensity factor, K-PR, under three different basic loading se quences involving compressive loads. The data of the entire experiment al program collapse onto a single 'master curve' which describes K-PR as a function of K-max and the unloading ratio UR. Load interaction ef fects are mainly due to the changes of the residual compressive stress state in front of the crack tip, while crack closure plays a minor pa rt. The results give an improved understanding of fatigue crack propag ation.